This post will discuss post curing options with an introduction to the science of transforming the mechanical properties of materials.

Why Should You Post Cure Your SLA 3D Prints?

When your SLA part is printed, it is on your build platform in a “green state.” This means that while parts have reached their final form, the polymerization reaction has not been fully completed and full the potential mechanical properties have not yet been reached. Light and heat will unlock this hidden potential in your 3D printed parts. We call this final process post curing.

Material properties, such as modulus can be enhanced with post curing. Each type of Formlabs resin requires unique post cure settings. The data shown in the above graph is derived from testing by Formlabs and provided for illustration purposes.

Post curing is a requirement for some of the Formlabs resins. Only after post curing will Engineering Resins reach their best functional form and Formlabs Castable Resin will burn out cleanly. Post curing is definitely mandatory for using biocompatible materials like the Formlabs Dental Resins.

Post curing is not striclty a requirement for Standard Resins, but it will still deliver benefits, improving strength and stability. Post cured parts are also generally easier to sand and paint, allowing you to achieve a smooth final surface.

The Science of Post Curing

We know that post curing improves material properties, but how does this work?

To give a basic explanation, exposure to light triggers the formation of additional chemical bonds within the 3D printed part, making the material stronger and stiffer in the process.

Formlabs’ new post curing unit, Form Cure, uses 405 nm light, while many other curing devices use UV light (wavelengths between 10 nm and 400 nm). Even sunlight can post cure parts, however the results will be dependent on weather conditions and a range of environmental variables.

Some post curing chambers also use heat. Heat accelerates the process to deliver a more complete bond formation in a shorter time, resulting in material properties that can not be achieved with light alone.

A Molecular-Level Look

Inside your 3D printing resin is a continuous network of various types of polymer chains (monomers and oligomers). The resin itself is one highly cross linked macromolecule (if you selected a spot anywhere on a 3D printed part and zoomed into the molecular level, you could follow the polymer chain to any other spot in that part).

While printed resin is one continuous molecule, there are still some open reactive groups that can be linked to strengthen the polymer network.

As more cross links form, material properties, such as modulus and tensile strength, improve. The process of post curing links these unreacted groups to bring a 3D printed part to its maximum material potential.

Post curing maximises material properties in SLA 3D printed parts through the controlled synergy of temperature and light. Some post curing units will also rotate for consistent exposure across the whole part.

Once molecules reach the optimum temperature, reactive groups will move close enough to bond with one another.

With each new cross link, the polymer network is further strengthened and material properties improved.

As additional cross links continue to form, the network slightly densifies creating minor shrinkage of the part. This is normal for any resin based 3D printed parts. PreForm, Formlabs’ free print file preparation software, automatically allows for this shrinkage to ensure your post cured prints are dimensionally accurate to your original 3D designs. This precise calibration is very important for applications including dental materials that require high levels of accuracy.

Choosing a Post Curing Method

There are many options for post curing, from curing simply with light only (natural sunlight, UV nail salons, cure boxes, etc.) to using both light and heat, such as Formlabs’ Form Cure or the MTC BBCure.

Many methods of post-curing exist, such as this UV nail salon.

There are a range of factors to consider when selecting which post-curing method is best for your prints:

Materials used: For each resin formulation there's a certain wavelength range that will best maximise its mechanical properties. For Formlabs materials specifically, we recommend purchasing a unit that uses 405 nm light, as Formlabs resins are uniquely engineered to work with Formlabs printers, which use 405 nm lasers in the 3D printing process.

Intended applications: For applications that require high levels of dimensional accuracy, you will need a curing unit tuned to the specific materials you are printing with. Such applications include prototyping products that need tight tolerances or dental applications that rely on precise fit (such as surgical guides or crown and bridge models). For applications where accuracy is less important, and tolerances are larger, a generic curing solution should be suitable.

Size and complexity: For small prints, a low cost UV nail salon can be an effective post curing tool. For larger and more complex parts, consider curing units that provide even exposure (through well balanced light placement, a rotating turntable, etc.) to ensure consistent curing across your 3D printed part.

Be aware that material properties can also vary with part geometry, print orientation, and print settings.

Speed requirements: Heat will speed up and optimises the post curing process. If speed is a concern, consider a unit that uses both light and heat to save time.

MTC BBCure: Standard and Dental versions now available from Redstack

The MTC BBCure Tech is the perfect UV curing station for Formlabs’ engineering resins, standard resins and Castable resin. With a footprint of 350mm x 350mm x 312 mm, the BBCure Tech fits on a desk easily. It has full 360° UV LEDs inside, which bathe models with a 402nm UV light source at a temperature of up to 60°C.

Combining the functionality of UV LEDs with heat, it creates an all in one curing station for post curing your parts and models printed with a Formlabs or similar SLA 3D printer.

Formlabs’ post-cure solution, Form Cure, is designed to optimize the properties of parts printed in Formlabs resins.

Formlabs goal was to develop a post curing solution that would simplify and optimise post curing processes for Formlabs materials.

Formlabs have run extensive tests to determine the most effective technology and developed optimal settings that work best for each of their resins. The Form Cure provides an intuitive, automated process for easy and convenient post curing.

Form Cure is a reliable, professional post curing solution engineered to help our users get the most out of their Form 2.

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